The present invention relates to an image forming apparatus configured to identify developer tanks of different types on a model-by-model basis or on a developer color basis for a single model.
Nowadays, multifunctional and diversified image forming apparatus are progressing. Such image forming apparatus use developer tanks of different types on a model-by-model basis. Image forming apparatus of the type capable of color printing use developer tanks containing respective of black (K), yellow (Y), magenta (M) and cyan (Cy) developers. For this reason, a factory and a service department are required to pay careful attention to fitting of removable developer tanks in respective correct positions. In the present conditions where such factory and service department must handle developer tanks of many types, it is highly possible that such developer tanks are fitted erroneously.
A prior-art technique serving as a hint for a solution of this problem is configured to determine whether or not an ink-containing cartridge is fitted to an ink-jet printer based on a time constant varying according to whether or not the cartridge is fitted, as disclosed in Japanese Patent Laid-Open Publication No. H05-254147.
Another relevant prior-art technique is configured to detect fitted condition and empty condition of an ink cartridge by an arrangement wherein the ink tank is provided with electrodes and an interface circuit disposed between these electrodes, as disclosed in Japanese Patent Laid-Open Publication No. 2003-237101.
However, either of the aforementioned prior-art techniques is configured to detect the fitted state of an ink cartridge and cannot identify the type of the cartridge fitted or detect whether or not the cartridge is properly fitted in its correct position. For this reason, even if such a technique is applied to an image forming apparatus to be fitted with developer tanks of various types, a problem remains unsolved that it is not possible to detect whether or not a proper developer tank is fitted in its correct position, though it is possible to detect whether or not each of the developer tanks is fitted.
Prior-art image forming apparatus include one which has a resistance type voltage divider circuit comprising a resistive element for identification disposed at a developer tank and another resistive element disposed on the apparatus body side and connected in series with the other. With the resistance type voltage divider circuit being applied with a fixed voltage, the developer tank is identified by detection of a voltage (divided voltage) across the opposite ends of the resistive element disposed at the developer tank.
With the apparatus adapted to identify a developer tank by means of such a resistance type voltage divider circuit, however, it is difficult to identify a number of developer tanks while securing sufficient resolving power and S/N. For example, in the case where 20 types of developer tanks are to be identified and an ordinary IC of which VCC is 5V is used as a divided voltage detection circuit, detection need be conducted with a precision of 0.25V per resistive element according to a simple calculation. If a margin of allowance, variability of resistive elements, noise and a like factor are taken into consideration, correct identification of each of the developer tanks is found to be practically very difficult.
A feature of the present invention is to provide an image forming apparatus, a developer tank and a method of identifying a developer tank, each of which allows developer tanks to be identified correctly with a sufficient margin of allowance.